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<p>Understanding the evolution of the Asian summer monsoon (ASM) on precessional timescales is essential for reconstructing the past Asian climate, understanding environmental changes, and anticipating future climate trends. However, existing marine and terrestrial proxy records show nearly antiphase relationships in ASM rainfall: terrestrial records vary in phase with Northern Hemisphere summer insolation (NHSI), whereas marine records vary inversely with it. This discrepancy has been explained that the ASM is driven either by NHSI or by Southern Hemisphere (SH) summer insolation, leading to a longstanding debate about its fundamental forcing mechanisms. Based on a transient climate simulation spanning the past 150 kyr, this study reveals that the apparent phase contrast between marine and terrestrial rainfall records primarily reflects spatially distinct rainfall responses over land and ocean regions. Through sensitivity experiments that separately isolate Northern Hemisphere and Southern Hemisphere insolation effects, we demonstrate that the land-sea rainfall contrast in the East Asian region is predominantly driven by NHSI. Enhanced NHSI warms the mid- to high-latitudes, leading to a northward shift of the westerly jet. This shift promotes poleward moisture transport and increases moist static energy, ultimately enhancing rainfall over northern China while reducing rainfall over Japan and adjacent coastal areas. For the South Asian region, both NH and SH insolation contribute to the land-sea rainfall contrast. Land rainfall increases are mainly attributed to NHSI, whereas reduced rainfall over the Bay of Bengal is closely linked to SH insolation. When boreal summer occurs at perihelion, the NHSI increase is accompanied by SH insolation increase. The rise in SH insolation weakens the Hadley circulation and the South Asian monsoon circulation, thereby suppressing evaporation and rainfall over the Bay of Bengal. This study elucidates distinct forcing mechanisms behind the land-sea rainfall contrast in East and South Asia. The findings help reconcile inconsistencies between marine and terrestrial proxy records and deepen our understanding of ASM dynamics on precessional timescales, offering valuable insights for interpreting paleoclimate archives and projecting future monsoon behavior.</p>

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Phase contrast in Asian summer monsoon rainfall between marine and terrestrial records on precessional timescales and their driving mechanisms

  • 期刊论文

  • 发表日期：

    2026年4月15日

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  • Qin Wen,
  • Tao Wang,
  • Zhengyu Liu,
  • Deliang Chen,
  • Jian Liu,
  • Liang Ning,
  • Mi Yan,
  • Zhaowei Jing,
  • Heng Liu,
  • Jing Lei,
  • Jiuyou Lu,
  • Xiao Zhang,
  • Qiuzhen Yin

摘要

Understanding the evolution of the Asian summer monsoon (ASM) on precessional timescales is essential for reconstructing the past Asian climate, understanding environmental changes, and anticipating future climate trends. However, existing marine and terrestrial proxy records show nearly antiphase relationships in ASM rainfall: terrestrial records vary in phase with Northern Hemisphere summer insolation (NHSI), whereas marine records vary inversely with it. This discrepancy has been explained that the ASM is driven either by NHSI or by Southern Hemisphere (SH) summer insolation, leading to a longstanding debate about its fundamental forcing mechanisms. Based on a transient climate simulation spanning the past 150 kyr, this study reveals that the apparent phase contrast between marine and terrestrial rainfall records primarily reflects spatially distinct rainfall responses over land and ocean regions. Through sensitivity experiments that separately isolate Northern Hemisphere and Southern Hemisphere insolation effects, we demonstrate that the land-sea rainfall contrast in the East Asian region is predominantly driven by NHSI. Enhanced NHSI warms the mid- to high-latitudes, leading to a northward shift of the westerly jet. This shift promotes poleward moisture transport and increases moist static energy, ultimately enhancing rainfall over northern China while reducing rainfall over Japan and adjacent coastal areas. For the South Asian region, both NH and SH insolation contribute to the land-sea rainfall contrast. Land rainfall increases are mainly attributed to NHSI, whereas reduced rainfall over the Bay of Bengal is closely linked to SH insolation. When boreal summer occurs at perihelion, the NHSI increase is accompanied by SH insolation increase. The rise in SH insolation weakens the Hadley circulation and the South Asian monsoon circulation, thereby suppressing evaporation and rainfall over the Bay of Bengal. This study elucidates distinct forcing mechanisms behind the land-sea rainfall contrast in East and South Asia. The findings help reconcile inconsistencies between marine and terrestrial proxy records and deepen our understanding of ASM dynamics on precessional timescales, offering valuable insights for interpreting paleoclimate archives and projecting future monsoon behavior.